This invention relates to the grinding of blades for turbines, compressors and the like in general and more particularly to an improved method and apparatus for carrying out such grinding.
In blades of this nature, the accuracy of the profile and quality of the surface are prerequisites for proper operation and optimum efficiency. Normally, great analytical and experimental effort is expended in developing blade profiles for given operating conditions. In addition to the aerodynamic and thermodynamic aspects of the blades, vibration and strength considerations such as a narrow bandwidth of resonance frequencies resulting from the profile or minimal notch effects place stringent requirements on the profile tolerance and surface roughness of the blades.
In order to insure that these requirements are met, it is typical to follow fabrication of the blade using chip removing apparatus and non-chip removing apparatus with finishing operations such as grinding, wet sanding, ball blasting and so on. Of these various finishing operations, in practice, belt grinding has been found to be the most efficient for contour grinding as well as surface finishing. Thus, it alone or in conjunction with other processes is an integral part of blade production.
In the grinding processes presently in use, the work piece is pushed by hand against the abrasive belt which moves over a contact pulley with the proper grinding velocity. The guidance of the work piece and the feed motion are also carried out by hand. This requires great skill, particularly to obtain accurate contour grinding of blades with compound curvature to the proper dimensions. However, interruptions of the grinding operation for gauging are necessary. In addition, the development of heat and the normally relatively short distance from the abrasive belt to the operations hand holding the work piece require that the operator wear partial gloves for safety reasons. Additional problems are caused when handling large and thus, usually relatively heavy blades. The impairment of the touch of the operator because of the weight of the blades and the necessity of wearing gloves is a factor in the ability to obtain accurate grinding.
In view of these various problems, the need for an improved method and apparatus which permits grinding of blades, including those of large weight, to a proper dimension in a simple manner becomes evident.